Jack Teixeira, 21, wore shackles and a prison uniform as he stood before a federal judge on Friday.
After a shout of “Love you, Jack” from a person in the courtroom, the defendant replied, “You too, Dad”.
Mr Teixeira faces up to 15 years in prison over charges of unauthorized transmission of defense information. He is also charged with the unauthorized removal and retention of classified documents. The airman faces up to 10 years in prison for the first charge, and up to five years in prison for the second.
The dozens of leaked documents had revealed US assessments of the war in Ukraine as well as sensitive secrets about American allies. The leaks embarrassed Washington and raised fresh questions over the security of classified information.
Mr Teixeira was arrested by armed FBI agents at his family home in Massachusetts on Thursday.
The judge ruled that the suspect qualifies for a public defender – a lawyer employed at public expense in a criminal trial for people who cannot afford legal fees.
Mr Teixeira remains in custody.
US President Joe Biden thanked law enforcement in a statement for their “rapid action” to investigate the source of the leaks. He said he has directed the US military and intelligence to secure and limit the distribution of any more sensitive information.
‘Top secret clearance’
The leaked intelligence material first appeared in a Discord chat room on which Mr. Teixeira is said to have been an administrator. Its members would often discuss geopolitical affairs and wars.
The affidavit provided by FBI Special Agent Patrick Lueckenhoff to the court stated that the suspect began posting the leaked documents sometime in December.
The initial leaks were in the form of paragraphs of text, according to the affidavit, but Mr Teixeira then moved on to posting photographs of documents in January.
It was not until intelligence material was posted outside the chat room group that Pentagon officials became aware of the leak, prompting a search for the culprit.
Mr Teixeira worked as an IT specialist in the intelligence wing of the Massachusetts National Guard, based at Otis Air National Guard Base in western Cape Cod.
The National Guard is a reservist wing of the US Air Force. They are not employed full-time in the military but can be deployed when necessary.
Mr Teixeira’s official title was cyber defense operations journeyman, according to the criminal complaint filed in the Boston court. He held the rank of Airman 1st Class – a relatively junior position.
The affidavit stated that Mr Teixeira held a “top secret” security clearance since 2021 and that he would have “signed a lifetime binding non-disclosure agreement” to take on his role.
Mr Luekenoff added the suspect “would have had to acknowledge that the unauthorized disclosure of protected information could result in criminal charges”.
The affidavit also alleged that Mr Teixeira used his government computer to search classified intelligence reporting for the word “leak” on 6 April – the day when public reporting about the documents first emerged.
Prosecutors alleged that Mr Teixeira searched the term to learn whether US intelligence had information on the identity of the person behind the leaks.
